After the discussion of the numerical simulation method based on the FDTD method and the PML technique, the motions of the charges and the electrical field lines were first employed to describe the radiation procedures of the pulse electromagnetic waves. Then the causes of how the charges are accelerated and how the motion status of the charges are maintained were further studied from the angle of interaction of charge and field. After these analyses, it was pointed out that the pulse radiation is due to the suddenly occurred time-varying electrical field (displacement current) in the open space. This view was further evidenced by two examples: one is the partly resistance loaded antenna, the other is the partly curved antenna. The radiation procedures of the pulse electromagnetic waves of many different situations were simulated throughout this paper with the contours and waveforms of electric field given. These figures are very helpful to the understanding of the radiation mechanism of the pulse electromagnetic waves.